1. Field Of The Invention
This invention relates to a self-sealing extrusion die and die ring and an associated extrusion process and more particularly to an extrusion process and die which minimizes "caving" in dies.
2. Background Information
It is well known to make extrusions using an extrusion press. A standard extrusion press is a massive device which consists of a movable billet container defining a cylindrical billet opening which receives a heated billet material to be extruded. The press further includes a die assembly, held in place by a die slide, and a platen against which the die slide and die assembly are positioned. For solid dies, the die assembly consists of a die ring which holds a die and a backer. The die contains the shape of the final extrusion. The extrusion press is equipped with a hydraulic ram which forces the material to be extruded against the die to form the extrusion.
The process of making an extrusion consists of loading a billet of material into the movable billet container, moving the billet container into contact with the die assembly and then forcing the material through a die and backer by means of the hydraulic ram to form the extrusion.
FIGS. 1 and 1A of the drawings show a crosssectional view of the prior art extrusion press. It can be seen that the billet container 10 has a billet opening 12 having a diameter "b" with a billet 14 and a dummy block 14a placed therein. The die assembly 15 consists of a die slide 16 which holds the bolster 17 and die ring 18. The die ring 18 contains the die backer 19 and the die 20. The die assembly 15 is supported by a platen 21 having a platen ring 22. As is well known, the platen 21 provides "back pressure" on the die assembly to counteract the force of the hydraulic ram 23 pushing the billet 14 through the die assembly 15 to form the extrusion 24.
The die 20 has a facing surface with a diameter of "d". As can be seen, diameter "d" is larger than the billet opening 12 diameter "b". Conventionally, the die facing surface diameter "d" is 93/8", whereas the billet opening diameter "b" is 73/8". These diameters will vary depending on the size of the extrusion press. Also, the die is designed to protrude from the die ring at "p" about 0.020 inches.
When the billet container is moved into contact with the die assembly as shown in FIGS. 1 and 1A, the combination of the larger diameter facing surface of the die and the fact that the die protrudes from the die ring means that the billet container forms an annular seal "s" on the die facing surface. This seal is necessary so that the aluminum to be extruded does not squirt out from an opening between the container and the die face, a phenomenon known as "flairing".
A major problem with traditional dies is a phenomenon known as "caving". Caving occurs because the entire force of the billet is concentrated in the center of the die. Over time, this will cause the center to be pushed in or "caved". As can be seen with the prior art extrusion method, the entire force of the billet is upon the center of the die facing surface. As is well known in the extrusion art, a small variation in the die facing surface can lead to major distortions in the extruded product.
There is a need for an extrusion process and an associated die and die ring that minimizes the problems associated with prior art extrusion methods. This process should resist caving of the die and thus avoid the problems associated with this phenomenon. Finally, the process should be adapted to be used on standard extrusion presses.